Returns a block of image data containing the specifed rectangular area, in the specified component, as a copy (see below). The rectangular area is specified by the coordinates and dimensions of the 'blk' object.

       <p>The area to return is specified by the 'ulx', 'uly', 'w' and 'h'
       members of the 'blk' argument. These members are not modified by this
       method.</p><p>The data returned by this method is always a copy of the internal
       data of this object, if any, and it can be modified "in place" without
       any problems after being returned. The 'offset' of the returned data is
       0, and the 'scanw' is the same as the block's width. See the 'DataBlk'
       class.</p><p>If the data array in 'blk' is <tt>null</tt>, then a new one is
       created. If the data array is not <tt>null</tt> then it must be big
       enough to contain the requested area.</p><p>The returned data always has its 'progressive' attribute unset (i.e
       false)</p>